Нашел, если кому надо:
Blob parameters
Testing NULL values in blob input parameters is easy. Blob parameters are
passed to UDF as a pointer to BLOB structure. If the parameter is NULL, then
blob_handle element of this structure will be zero.
Full BLOB structure definition/description can be found either in Developer's
Guide or in jrd/val.h file (IB/FB source code) or in include/ibase.h file
(Firebird only).
Example
This function will return either blob size, or -1 if the parameter is NULL
type
TBlob = record
GetSegment : Pointer;
BlobHandle : ^Integer;
SegmentCount : LongInt;
MaxSegmentLength : LongInt;
TotalSize : LongInt;
PutSegment : Pointer;
end;
PBlob = ^TBlob;
function TEST_BlobSize(inBlob: PBlob): integer; cdecl;
begin
Result := -1;
if (not Assigned(inBlob)) or
(not Assigned(inBlob^.BlobHandle)) then Exit;
Result := inBlob^.TotalSize;
end;
DECLARE EXTERNAL FUNCTION TEST_BlobSize
BLOB
RETURNS INTEGER BY VALUE
ENTRY_POINT 'TEST_BlobSize' MODULE_NAME 'UDF_Examples';
CREATE TABLE TAB3 (I INTEGER, B BLOB);
INSERT INTO TAB3 (I,B) VALUES (1, 'abc');
INSERT INTO TAB3 (I,B) VALUES (2, '');
INSERT INTO TAB3 (I,B) VALUES (3, NULL);
/* Note: Firebird can insert strings to blob fields directly. */
/* With InterBase you may need to use UDF for String->Blob conversion. */
SELECT I, TEST_BlobSize(B) FROM TAB3;
I TEST_BLOBSIZE
======= =============
1 3
2 0
3 -1
С наилучшими пожеланиями, Oleg Prosvetov.
